Conformational study of chiral penicillamine ligand on optically active silver nanoclusters with IR and VCD spectroscopy

The conformation of chiral d-/l-penicillamine (d-/l-Pen) adsorbed on optically active silver nanoclusters with a mean core diameter of about 1.1 nm was investigated by infrared (IR) and vibrational circular dichroism (VCD) spectroscopy. IR spectra of the d-/l-Pen-protected nanoclusters in D2O/CD3OD solution are essentially identical, but the VCD exhibits a mirror image relationship indicating that these species have enantiomeric relationship. The experimental IR and VCD spectra are compared with the calculated ones for different model conformers at the DFT/B3PW91 level. The analysis in the spectral region of νasym(COO−) and δsym(NH2) modes reveals significant shortcomings when comparing with vacuum calculations. We then take a bulk solvent effect into account in the theoretical calculations to obtain better agreement, resulting in the establishment of a preferential conformation of chiral penicillamine on the silver nanocluster surface.